Technical Field
Devices for conversion of solar energy to electrical energy, and methods of fabricating such devices. In particular, a solar cell including constituents from volcanic ash, and related methods of fabrication of the solar cell.
Description of Related Art
A nano-crystalline dye sensitized solar cell, or “DSSC,” is a photo electrochemical cell that uses photons to excite electrons in organic dyes. This process, in turn, creates electrical power. Unlike conventional photovoltaic (PV) cells that use silicon as a primary ingredient, a typical DSSC uses titanium dioxide (TiO2) as a constituent in its construction. In addition to TiO2, DSSC technology relies upon carbon or graphite as additional elements in its operation. The DSSC may emerge as the next generation of PV cells to produce cheaper sources of solar energy. The DSSC has the potential to provide power efficiency, low cost of manufacturing, and a relatively short payback time in energy production.
The promise of DSSC technology, however, faces technical challenges. For example, conventional DSSC devices have lower efficiency values than conventional PV cells. In contrast to conventional cells, the DSSC is a photoelectrochemical cell. FIG. 1 depicts a cross-sectional schematic view of a portion conventional dye sensitized solar cell 10. A typical DSSC is comprised of a series of thin film coatings (also referred to herein as layers) formed upon a glass substrate 20. The layers include a first conductive layer 30 operable as an anode of the cell, a charge blocking layer 40, a hole conducting layer 50, and a second conductive layer 60 operable as an anode of the cell. The device 10 may include an additional transparent protective layer (not shown), such as a glass layer, that is contiguous with the second conductive layer 60.
The first and second conductive layers that function as electrodes are comprised of light transmissive conductive materials, such as tin dioxide (SnO2). The charge blocking layer 40 is also of a light transmissive material. In that manner, light that is incident on the cell 10 may propagate through conductive layer 60; and optionally, depending upon the positioning of the cell in its environment, also through conductive layer 30 and blocking layer 40.
The hole transporting layer 50 is comprised of one or more sub-layers containing a suspension of nanometer size particles 52 of titanium dioxide (TiO2) that is distributed uniformly therethrough. The titanium dioxide particles are in close proximity to and are exposed to an organic dye 54, such as an organometallic complex or a green chlorophyll derivative, also contained in the one or more sublayers. A variety of other natural dyes may be utilized, provided that they include a chemical group that can attach to the semiconductor (TiO2) particle surface and have energy levels at the proper band levels necessary for electron injection and sensitization. In the operation of the cell, a single layer of dye molecules attaches to each particle of the TiO2 and acts as an absorber of incident light. A liquid electrolyte (not shown), such as iodine, is applied to the TiO2-containing sublayer(s) and percolates into them. A counter electrode wafer of conductive glass coated with graphite, carbon, or platinum, and which includes the second conductive layer 60, completes the device 10.
It is to be understood that for the sake of brevity, the above description and the schematic diagram of cell 10 in FIG. 1 have been simplified. Further details on the structure and operation of a conventional DSSC may be found in, e.g., U.S. Pat. No. 5,350,644 of Graetzel et al., the disclosure of which is incorporated herein by reference.
The conversion efficiency of a solar cell is the maximum electrical power output divided by the incoming solar power on the same area. Not all of the energy from sunlight can be converted into electrical energy. Some of the sunlight is converted into heat. To the best of the Applicant's knowledge, the overall sunlight to electrical energy conversion efficiency of a DSSC using the best dyes currently available is 7 to 10% under direct sunlight. This is to be compared to 0.5% for natural photosynthesis and 12 to 20% for commercial silicon solar cell modules. One process that limits the efficiency of a DSSC is the transfer of the injected electron to the oxidized mediator before the electron has been collected and passed through the load and counter electrode.
Even with these limitations, the spectrum of light utilized by conventional dyes indicates that a DSSC of at least 10% efficiency could be realized at a cost of $0.60 per watt. This is competitive with conventional power generation and illustrates the promise of DSSC technology. DSSC technology is particularly viewed as a promising source of energy for developing areas because of its reduced costs. However, the discovery of alternative materials that produce improved energy conversion and environmentally sensitive results are needed, and would have a highly beneficial impact. Such a breakthrough in DSSC design would open up a new source of affordable and sustainable power.